Automatically determining the location of a caller during an emergency is crucial to the function of an emergency calling system. Thus, in the United States, the National Emergency Number Association (NENA) released VOIP Enhanced 911 (E911) standards. The VOIP E911 provides a standard for VOIP service providers to determine a physical location of VOIP devices connected to the service provider's network. The VOIP E911 emergency-calling system associates a physical address with the calling party's telephone number. Similarly, in the United Kingdom, NICC released ND1638 VOIP emergency call standards and the European Union released emergency call standards for VOIP emergency calls made within the European Union.
VOIP devices (e.g., phones or computers) transmit phone calls over the internet, typically by using Session Initiation Protocol (SIP) of the Request For Comments (RFC) standards. VOIP devices can also transmit calls over a Global System for Mobile Communication (GSM) mobile phone network by connecting to the GSM via an appropriate interface (e.g., interworking function and/or a gateway). For example, a WAG can translate SIP messages into a format that is understood by a MSC of a GSM. In addition to providing call handling to VOIP devices, the GSM can also provide call services to VOIP devices.
Providing emergency services when a VOIP device is connected to the MSC via a WAG is problematic because an MSC typically receives device location information from a Radio Access Network (RAN), and VOIP devices do not communication with RANs. The MSC has no mechanism for obtaining a VOIP devices location information. Therefore, it is desirable for an MSC to obtain location information of a VOIP device.